I knew array_filter existed and what it was all about since before, however I started working with something requiring array_map first, all well and OK, array_map looks like this: array_map('callback', Array). So then I assumed I could use array_filter in the same fashion, big mistake.

He was caught by the parameter order difference between the two and problems with how the callbacks worked. In the end, he he spent an hour to create a function to search an array for a partial match and didn't even end up using the array functions (opting for calls to stripos instead).